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Characterization of Phosphonium Ionic Liquids with Emphasis on Mass Spectrometry and Chromatography 1
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Ted Chang , Allan Robertson , Eduardo Kamenetzky , Chermeine Rivera , Liying Du , Douglas Harris , Michael Piquette , Donato Nucciarone , and Christopher Crutchfield 1
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Cytec Research Center, Cytec Industries, 1937 West Main Street, Stamford, C T 06904 Cytec Canada Inc., 9061 Garner Road, Niagara Falls, Ontario L2E 6S5, Canada 2
Introduction The majority of ionic liquid publications deal the synthesis, properties and applications of ionic liquids. This paper focuses on characterization and analysis o f ionic liquids, more specifically on trace analysis. Cytec is a major producer of phosphonium ionic liquids and believes that as industrial applications and demand for ionic liquids continues to grow, so will the needs for accurate analytical methods to determine trace quantities of various ionic liquids in reactions streams as well as impurity ions in the ionic liquids. In this paper, we will address some of these issues. Product assays usually require identification and analysis to the extent of 0.1% for various impurities-physical properties of ionic liquids are particularly sensitive to low levels of anion impurities . In addition, toxic and carcinogenic impurities need to be determined to the ppm level or to the ppb level depending on their chemical/biological toxicity. If ILs are to be used as solvents or as catalysts, their residual amounts in the products have to be analyzed accurately. In degradation studies, U V measurement alone is not only insufficient but often also includes false positives. The degradation products need to be identified and determined individually. For environmental and toxicology studies, analytical methods are often required with sub-ppm or ppb sensitivity 1
© 2007 American Chemical Society
In Ionic Liquids IV; Brennecke, Joan F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
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depending on regulations. In industrial productions, the discharge of waste water to natural water is a highly regulated issue. As ionic liquid manufacturers, we are obligated to develop methods not only to assay the products but also to determine their ultimate fate in the environment. For these reasons, applications of mass spectrometric and chromatographic techniques for the analysis of phosphonium ionic liquids are being investigated.
Phosphonium Ionie Liquids Phosphonium salts, especially halides, have been available commercially for many years. The main applications being used as phase transfer catalysts, in resin curing or as biocides. They are typically made by quaternizing a tertiary alkylphosphine with a chloro, bromo or iodo alkane. The resulting phosphonium halides can be used as ionic liquids or as usually is the case, they are converted by various metatheses to non-halogen phosphonium ionic liquids. Alternatively, tertiary alkylphosphines can directly react with active esters such as tosylates, sulfates, phosphates or mesylates to form"non-halogenated salts" directly. Detailed procedures for the syntheses of many phosphonium ILs have been summarized by Downard etal. . Phosphonium ILs are also the subject of many other researchers. J. Knifton published numerous papers and patents on petrochemical applications using "molten phosphonium salts" as solvents . Phosphonium salts have been successfully used for Heck, Suzuki and esterification reactions . Hoffmann reported surprisingly high C 0 solubility in phosphonium ILs . The Wilkes group demonstrated the unusual ability of alkylphosphonium cations to "liquefy" very high molecular weight salts . More recently, Clyburne demonstrated the surprising stability of phosphonium salts toward strong bases such as Grignard reagents and borane . Pernak has prepared and investigated electrochemical properties of several series of phosphonium salts . Livingston has addressed the important issue of removing trave levels of ionic liquids from reactor products by use of unique "molecular f i l t e r s " . A unique series of phosphonium ILs with amino acids derived anions were reported at the March, 2006 Atlanta A C S Ionic Liquid Symposium by Ohno . At the same meeting, McCleskley discussed para-magnetic properties of phosphonium salts containing transition metal anions . The all-important aspect of bioactivity has been addressed by Pernak and Stock . C Y P H O S IL® is the trade name of Cytec phosphonium ILs. Table 1 lists the phosphonium ILs used in this study. The table includes abbreviations used in the L C / M S study (PI, P2, etc), commercial names (CYPHOS IL 101, C Y P H O S IL 102, etc), and cations and their anions. The table also includes imidazolium ILs used in this study. 2
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In Ionic Liquids IV; Brennecke, Joan F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
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Table I. Ionic Liquids used in this Study Abbr
CYPHOS IL®
R,R,R,R'-P
Anion
PI P2 P3 P4 P5 P6 P7
IL 106 IL164 IL 167 IL101 IL163 IL104 IL109
C4,C4,C4,C1-P C4,C4,C4,C4-P C4,C4,C4,C14-P C6,C6,C6,C14-P C4,C4,C4,C4-P C6,C6,C6,C14-P C6,C6,C6,C14-P
P8 P9 P10 Pll P12 P13
IL 105 IL162 IL107 IL102 IL110 IL202
C6,C6,C6,C14-P C4,C4,C4,C16-P C4,C4,C4,C4-P C6,C6,C6,C14-P C6,C6,C6,C14-P C6,C6,C6,C14-P
tosylate chloride chloride chloride bromide (C8,C8)phosphinate bis(trifluoromethane sulfony)lamide dicyanamide bromide dibutylphosphate bromide hexafluorophosphate decanoate
EMIm BMIm EMIm pyridinium
chloride chloride trifluoromethanesulfonate p-toluenesulfonate
Iml Im2 Im3 Pyl
General Characterization Techniques TGA Thermal stability is an important property of ILs, and T G A usually is the first analytical technique employed for characterization. It has been repeated pointed out that dynamic T G A does not reflect the true thermal stability of ILs . Thermal decomposition of a compound commences at the onset of weight loss and not the normally quoted inflection point of the derivative of T G A curve. Static T G A is a better technique to reflect this onset of thermal decomposition, which is typically 80-100°C lower than the inflection point of T G A curve. Figure 1 compares the static T G A of IL101 and B M I m under air and Figure 2 compares the static T G A of IL101 and B M I m in nitrogen. The inflection point of dynamic T G A for IL 101 is 350°C under air and 375°C under nitrogen. However, as can be seen in Figure 1, both IL101 and BMIm lost approximately 10% in 4 hours at 180°C. IL101 was more stable than B M I m at higher 22
In Ionic Liquids IV; Brennecke, Joan F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
In Ionic Liquids IV; Brennecke, Joan F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
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IL101 (P4) Solid lines: 180°C,240°C
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240
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180 C, Air
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150 C, Air
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270 C, Air
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240 C, Air
Time (Minutes)
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minutes to obtain the respective isothermic temperature.
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1-Butyl-3-methylîmidazolium chloride, 94128
320 C, Air
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B M I m chloride Solid lines: 180°C, 240°C
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Isothermic Runs Performed in Air of S19648-40D,
Figure 1. Thermal Stability, Static TGA under Air
Time (Minutes)
I ! 111111 90
270'C, Air
J11111111
!! 120
f rwicr - α » IUIIO uvyni a i « ν ν ariw i c i n c
